Hopes have dimmed that Congress would act quickly to rescue homeowners at risk of foreclosure after key Republican and Democratic negotiators in the Senate said they could not reach agreement on a plan. Talks broke down between aides to Senate Banking Committee Chairman Christopher J. Dodd (D-Conn.) and the senior Republican on his committee, Richard C. Shelby (Ala.), aides said. The two camps had been trying for more than a month to develop a bipartisan proposal to ease the nation's housing crisis.